Process for the production of paper

ABSTRACT

The present invention relates to process for the production of paper from a suspension containing cellulosic fibers, and optional fillers, comprising adding to the suspension drainage and retention aids comprising a cationic organic polymer and anionic microparticulate material, forming and dewatering the suspension on a wire, wherein the cationic organic polymer has a non-aromatic hydrophobic group. The invention further relates to a cationic vinyl addition polymer comprising in polymerized form at least one non-cationic monomer having a non-aromatic hydrophobic group and at least one cationic monomer.

[0001] This invention relates to papermaking and more specifically to aprocess for the production of paper in which a cationic organic polymerhaving a hydrophobic group and an anionic microparticulate material areadded to a papermaking stock. The process provides improved drainage andretention.

BACKGROUND

[0002] In the papermaking art, an aqueous suspension containingcellulosic fibres, and optional fillers and additives, referred to asstock, is fed into a headbox which ejects the stock onto a forming wire.Water is drained from the stock, through the forming wire so that a wetweb of paper is formed on the wire, and the web is further dewatered anddried in the drying section of the paper machine. Water obtained bydewatering the stock, referred to as white water, which usually containsfine particles, e.g. fine fibres, fillers and additives, is usuallyrecirculated in the papermaking process. Drainage and retention aids areconventionally introduced into the stock in order to facilitate drainageand increase adsorption of fine particles onto the cellulosic fibres sothat they are retained with the fibres on the wire. Cationic organicpolymers like cationic starch and cationic acrylamide-based polymers arewidely used as drainage and retention aids. These polymers can be usedalone but more frequently they are used in combination with otherpolymers and/or with anionic microparticulate materials such as, forexample, anionic inorganic particles like colloidal silica andbentonite.

[0003] U.S. Pat. Nos. 4,980,025; 5,368,833; 5,603,805; 5,607,552; and5,858,174; as well as International Patent Application No. WO 97/18351disclose the use of cationic and amphoteric acrylamide-based polymersand anionic inorganic particles as stock additives in papermaking Theseadditives are among the most efficient drainage and retention aids nowin use. Similar systems are disclosed in European Patent Application No.805,234.

THE INVENTION

[0004] According to the present invention it has been found thatimproved drainage and retention can be obtained by using drainage andretention aids comprising a cationic organic polymer having ahydrophobic group and an anionic microparticulate material. Morespecifically, the present invention relates to a process for theproduction of paper from a suspension containing cellulosic fibres, andoptional fillers, which comprises adding to the suspension a cationicorganic polymer and an anionic microparticulate material, forming anddewatering the suspension on a wire, wherein the cationic organicpolymer has a non-aromatic hydrophobic group. In a preferred aspect ofthe invention, the process further comprises forming and dewatering thesuspension on a wire to obtain a wet web containing cellulosic fibres,or paper, and white water, recirculating the white water and optionallyintroducing fresh water to form a suspension containing cellulosicfibres, and optional fillers, to be dewatered to form paper, wherein theamount of fresh water introduced is less than 30 tons per ton of drypaper produced. The invention thus relates to a process as furtherdefined in the claims.

[0005] The process of this invention results in improved drainage and/orretention and hereby the present process makes it possible to increasethe speed of the paper machine and to use lower a dosage of additives togive a corresponding drainage and retention effect, thereby leading toan improved papermaking process and economic benefits. The process ofthis invention is suitably used for the treatment of cellulosicsuspensions in closed mills wherein the white water is repeatedlyrecycled with the introduction of only low amounts of fresh water. Theprocess is further suitably applied to papermaking processes usingcellulosic suspensions having high salt contents, and thus having highconductivity levels, for example processes with extensive white waterrecycling and limited fresh water supply and/or processes using freshwater having high salt contents.

[0006] The cationic organic polymer having a hydrophobic group accordingto this invention, herein also referred to as “main polymer”, can belinear, branched or cross-linked, e.g. in the form of a microparticulatematerial, preferably essentially linear. Preferably the main polymer iswater-soluble or water-dispersable. The hydrophobic group of the mainpolymer is non-aromatic and it can be a pendent group attached to thepolymer backbone (main chain) or, preferably, a hydrophobic groupattached to a heteroatom, e.g. nitrogen or oxygen, the nitrogenoptionally being charged, which heteroatom, in turn, can be attached tothe polymer backbone, for example via a chain of atoms. The hydrophobicgroup has at least 2 and usually at least 3 carbon atoms, suitably from3 to 12 and preferably from 4 to 8 carbon atoms. The hydrophobic groupis suitably a hydrocarbon chain. Examples of suitable hydrophobic groupsinclude linear, branched and cyclic alkyl groups like ethyl; propyl,e.g. n-propyl and iso-propyl; butyl, e.g. n-butyl, iso-butyl andt-butyl; pentyl, e.g. n-pentyl, neo-penyl and iso-pentyl; hexyl, e.g.n-hexyl and cyclohexyl; heptyl, e.g. n-heptyl and cycloheptyl, octyl,e.g. n-octyl; nonyl, e.g. n-nonyl; decyl, e.g. n-decyl; undecyl, e.g.n-undecyl and dodecyl, e.g. n-dodecyl. The linear and branched chainalkyl groups are generally preferred.

[0007] The main polymer can be selected from homopolymers and copolymersprepared from one or more monomers comprising at least one monomerhaving a hydrophobic group, suitably an ethylenically unsaturatedmonomer, and the main polymer is preferably a vinyl addition polymer.The term “vinyl addition polymer”, as used herein, refers to a polymerprepared by addition polymerization of vinyl monomers or ethylenicallyunsaturated monomers which include, for example, acrylamide-based andacrylate-based monomers. According to a first embodiment of thisinvention, suitable main polymers include cationic vinyl additionpolymers obtained by polymerizing a cationic monomer having anon-aromatic hydrophobic group or a monomer mixture comprising such amonomer. Preferably the cationic monomer having a non-aromatichydrophobic group is represented by the general formula (I):

[0008] wherein R₁ is H or CH₃; R₂ and R₃ are each H or, preferably, analkyl group having from 1 to 3 carbon atoms, suitably 1 to 2 carbonatoms; A is O or NH; B is an alkylene group of from 2 to 8 carbon atoms,suitably 2 to 4 carbon atoms, or a hydroxy propylene group; R₄ is asubstituent containing a hydrophobic group, suitably a non-aromatichydrocarbon group containing at least 2 carbon atoms, suitably from 3 to12 and preferably from 4 to 8 carbon atoms; and X⁻ is an anioniccounterion, usually a halide like chloride. The group R₄ usuallycomprises and, preferably, is selected from any of the linear, branchedor cyclic alkyl groups mentioned above and the total number of carbonatoms of the groups R₂, R₃ and R₄ is usually at least 4, suitably atleast 5 and preferably at least 6. Examples of suitable cationicmonomers having a non-aromatic hydrophobic group include(meth)acryloxyethyl-N,N-dimethyl-N-n-butylammonium chloride,(meth)acryloxyaminoethyl-N,N-dimethyl-N-n-butylammonium chloride,(meth)acryloxypropyl-N, N-dimethyl-N-t-butyl-ammonium chloride,(meth)acryloxyaminopropyl-N,N-dimethyl-N-t-butylammonium chloride,(meth)acryloxyaminopropyl-N,N-dimethyl-N-n-hexylammonium chloride,(meth)acryloxyethyl-N,N-dimethyl-N-n-hexylammonium chloride,(meth)acrytoxyethyl-N,N-dimethyl-N-methylcyclohexylammonium chloride,and (meth)acryloxyaminopropyl-N,N-dimethyl-N-methylcyclohexylammoniumchloride.

[0009] The main polymer can be a homopolymer prepared from a cationicmonomer having a non-aromatic hydrophobic group or a copolymer preparedfrom a monomer mixture comprising a cationic monomer having anon-aromatic hydrophobic group and one or more copolymerizable monomers.Suitable copolymerizable non-ionic monomers include monomers representedby the general formula (II):

[0010] wherein R₁ is H or CH₃; A is O or NH; B is an alkylene group offrom 2 to 8 carbon atoms, suitably 2 to 4 carbon atoms, or a hydroxypropylene group or, alternatively, A and B are both nothing wherebythere is a single bond between C and N (O═C—NR₅R₆); R₅ and R₆ are each Hor a substituent containing a hydrophobic group, suitably a hydrocarbongroup, preferably alkyl, having from 1 to 6, suitably from 1 to 4 andusually from 1 to 3 carbon atoms. Examples of suitable copolymerizablemonomers of this type include (meth)acrylamide; acrylamide-basedmonomers like N-alkyl (meth)acrylamides and N,N-dialkyl(meth)acrylamides, e.g. N-n-propylacrylamide, N-isopropyl(meth)acrylamide, N-n-butyl (meth)acrylamide, N-isobutyl(meth)acrylamide and N-t-butyl (meth)acrylamide; and dialkylaminoalkyl(meth)acrylamides, e.g. dimethylaminoethyl (meth)acrylamide,diethylaminoethyl (meth)acrylamide, dimethylaminopropyl (meth)acrylamideand diethylaminopropyl (meth)acrylamide; acrylate-based monomers likedialkylaminoalkyl (meth)acrylates, e.g. dimethylaminoethyl(meth)acrylate, diethylaminoethyl (meth)acrylate, t-butylaminoethyl(meth)acrylate and dimethylaminohydroxypropyl acrylate; and vinylamides,e.g. N-vinylformamide and N-vinylacetamide. Preferred copolymerizablenon-ionic monomers include acrylamide and methacrylamide, i.e.(meth)acrylamide, and the main polymer is preferably an acrylamide-basedpolymer.

[0011] Suitable copolymerizable cationic monomers include the monomersrepresented by the general formula (III):

[0012] wherein R₁ is H or CH₃; R₂ and R₁ are each H or, preferably, analkyl group having from 1 to 3 carbon atoms, suitably 1 to 2 carbonatoms; A is O or NH; B is an alkylene group of from 2 to 8 carbon atoms,suitably 2 to 4 carbon atoms, or a hydroxy propylene group; R₇ is H, ahydrocarbon group, suitably alkyl, having from 1 to 3 carbon atoms,suitably 1 to 2 carbon atoms, or a substituent containing an aromaticgroup, suitably a phenyl or substituted phenyl group, which can beattached to the nitrogen by means of an alkylene group usually havingfrom 1 to 3 carbon atoms, suitably 1 to 2 carbon atoms, for example abenzyl group (—CH₂—C₆H₅) or a phenylethyl group (—CH₂—CH₂—C₆H₅); and X⁻is an anionic counterion, usually methylsulphate or a halide likechloride. Examples of suitable cationic copolymerizable monomers includeacid addition salts and quaternary ammonium salts of thedialkylaminoalkyl (meth)acrylamides and dialkylaminoalkyl(meth)acrylates mentioned above, usually prepared using acids like HCl,H₂SO₄, etc., or quaternizing agents like methyl chloride, dimethylsulphate, benzyl chloride, etc.; and diallyldialkylammonium halides likediallyidimethylammonium chloride. Copolymerizable anionic monomers likeacrylic acid, methacrylic acid, various sulfonated vinyl additionmonomers, etc. can also be employed and, preferably, in minor amounts.

[0013] According to a second embodiment of this invention, suitable mainpolymers include cationic vinyl addition polymers obtained bypolymerizing a monomer mixture comprising at least one non-cationicethylenically unsaturated monomer having a non-aromatic hydrophobicgroup and at least one cationic ethylenically unsaturated monomer, thenon-aromatic hydrophobic group being as defined above, and thisinvention further relates to a cationic vinyl addition polymer having anon-aromatic hydrophobic group, its preparation and use, as furtherdefined in the claims. Suitable non-cationic monomers having anon-aromatic hydrophobic group include non-ionic monomers, preferably anon-ionic monomer represented by the general formula (IV):

[0014] wherein R₁ is H or CH₃; A is O or NH; B is an alkylene group offrom 2 to 8 carbon atoms, suitably 2 to 4 carbon atoms, or a hydroxypropylene group or, alternatively, A and B are both nothing wherebythere is a single bond between C and N (O═C—NR₈R₉); R₈ and R₉ are each Hor a substituent containing a hydrophobic group, suitably a hydrocarbongroup, preferably alkyl, having from 1 to 6 carbon atoms, at least oneof R₈ and R₉ being a substituent containing a hydrophobic group,suitably an alkyl group, having from 2 to 6 and preferably 3 to 4 carbonatoms. The total number of carbon atoms of the groups R₈ and R₉ isusually at least 2, suitably at least 3 and notably from 3 to 6.Examples of suitable copolymerizable monomers of this type includeacrylamide-based monomers like N-alkyl (meth)acrylamides, e.g. N-ethyl(meth)acrylamide, N-n-propyl (meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl (meth)acrylamide, N-t-butyl(meth)acrylamide, N-isobutyl (meth)acrylamide, N-n-butoxymethyl(meth)acrylamide, and N-isobutoxymethyl (meth)acrylamide;N-alkylaminoalkyl (meth)acrylamides; N,N-dialkylaminoalkyl(meth)acrylamides, as well as acrylate-based monomers likeN-alkylaminoalkyl (meth)acrylates and N,N-dialkylaminoalkyl(meth)acrylates, e.g. t-butylamino-2-ethyl (meth)acrylate.

[0015] Further suitable non-cationic monomers having a non-aromatichydrophobic group include non-ionic monomers represented by the generalformula (V):

[0016] wherein R₁ is H or CH₃; A is O or NH; B is an alkylene group offrom 2 to 4 carbon atoms, suitably 2 to 3 carbon atoms, preferablyethylene (—CH₂—CH₂—) or propylene (—CH₂—CH(CH₃)— or —CH(CH₃)—CH₂—); n isan integer of at least 1, suitably from 2 to 40 and preferably 3 to 20;R₁₀ is a substituent containing a hydrophobic group, suitably alkyl,having at least 2 carbon atoms, suitably from 3 to 12 and preferablyfrom 4 to 8 carbon atoms. Examples of suitable copolymerizable monomersof this type include alkyl (mono-, di- and polyethyleneglycol)(meth)acrylates and alkyl (mono-, di- and polypropyleneglycol)(meth)acrylates, e.g. ethyltriglycol (meth)acrylate and butyldiglycol(meth)acrylate.

[0017] The cationic monomer can be selected from any of the cationicmonomers mentioned above, including the cationic monomers represented bythe general formulae (I) and (III) as well as diallyldialkylammoniumhalides like diallyidimethylammonium chloride. The monomer mixtureaccording to the second embodiment may also comprise othercopolymerizable monomers such as, for example, the non-ionic monomersrepresented by the general formula (II) above which may not have ahydrophobic group, suitably acrylamide and methacrylamide, and theanionic monomers mentioned above.

[0018] Main polymers according to this invention can be prepared from amonomer mixture generally comprising from 1 to 99 mole %, suitably from2 to 50 mole % and preferably from 5 to 25 mole % of monomer having anon-aromatic hydrophobic group, and from 99 to 1 mole %, suitably from98 to 50 mole % and preferably from 95 to 75 mole % of othercopolymerizable monomers which preferably comprises acrylamide ormethacryl-amide ((meth)acrylamide), the monomer mixture suitablycomprising from 98 to 50 mole % and preferably from 95 to 75 mole % of(meth)acrylamide, the sum of percentages being 100. According to thefirst embodiment of this invention, the monomer having a non-aromatichydrophobic group is cationic. According to the second embodiment ofthis invention, the monomer having a non-aromatic hydrophobic group isnon-cationic and the monomer mixture thus also comprises acopolymerizable cationic monomer which suitably is present in an amountof from 2 to 50 mole % and preferably from 5 to 25 mole %.

[0019] The main polymer according to this invention can be prepared bypolymerization of monomers in known manner and the polymerization issuitably carried out in an aqueous or inverse emulsion phase. Themonomer(s) used, including the monomer having a hydrophobic groupdescribed above, are preferably at least in part soluble in the aqueousphase. Polymerization processes are generally known in the art andreference is made to Encyclopedia of Polymer Science and Engineering,Vol. 1-18, John Wiley & Sons, 1985, which is hereby incorporated hereinby reference. The polymerization is suitably initiated in an aqueousphase containing monomers, a conventional free-radical polymerizationinitiator and optionally chain-transfer agent for modifying themolecular weight of the polymer, and is suitably carried out in theabsence of oxygen in an inert gas atmosphere, for example undernitrogen. The polymerization suitably takes place under stirring attemperatures between 20 and 100° C., preferably between 40 and 90° C.

[0020] Usually the charge density of the main polymer is from 0.2 to 5.0meqv/g of dry polymer, suitably from 0.6 to 3.0. The weight averagemolecular weight of synthetic main polymers is usually at least about500,000, suitably above about 1,000,000 and preferably above about2,000,000. The upper limit is not critical; it can be about 30,000,000,usually 25,000,000 and suitably 20,000,000.

[0021] The main polymer of this invention may be in any state ofaggregation such as, for example, in solid form, e.g. powders, in liquidform, e.g. solutions, emulsions, dispersions, including saltdispersions, etc. When being added to the stock, the main polymer issuitably in liquid form, e.g. in the form of an aqueous solution ordispersion.

[0022] The anionic microparticulate material according to this inventioncan be selected from inorganic and organic particles. Anionic inorganicparticles that can be used according to the invention include anionicsilica-based particles and clays of the smectite type. It is preferredthat the anionic inorganic particles are in the colloidal range ofparticle size. Anionic silica-based particles, i.e. particles based onSiO₂ or silicic acid, are preferably used and such particles are usuallysupplied in the form of aqueous colloidal dispersions, so-called sols.Examples of suitable silica-based particles include colloidal silica anddifferent types of polysilicic acid. The silica-based sols can also bemodified and contain other elements, e.g. aluminium and/or boron, whichcan be present in the aqueous phase and/or in the silica-basedparticles. Suitable silica-based particles of this type includecolloidal aluminium-modified silica and aluminium silicates. Mixtures ofsuch suitable silica-based particles can also be used. Drainage andretention aids comprising suitable anionic silica-based particles aredisclosed in U.S. Pat. Nos. 4,388,150; 4,927,498; 4,954,220; 4,961,825;4,980,025; 5,127,994; 5,176,891; 5,368,833; 5,447,604; 5,470,435;5,543,014; 5,571,494; 5,573,674; 5,584,966; 5,603,805; 5,688,482; and5,707,493; which are hereby incorporated herein by reference.

[0023] Anionic silica-based particles suitably have an average particlesize below about 50 nm, preferably below about 20 nm and more preferablyin the range of from about 1 to about 10 nm. As conventional in silicachemistry, the particle size refers to the average size of the primaryparticles, which may be aggregated or non-aggregated. The specificsurface area of the silica-based particles is suitably above 50 m²/g andpreferably above 100 m²/g. Generally, the specific surface area can beup to about 1700 m²/g and preferably up to 1000 m²/g. The specificsurface area can be measured by means of titration with NaOH in knownmanner, e.g. as described by Sears in Analytical Chemistry 28(1956):12,1981-1983 and in U.S. Pat. No. 5,176,891. The given area thus representsthe average specific surface area of the particles.

[0024] In a preferred embodiment of the invention, the anionic inorganicparticles are silica-based particles having a specific surface areawithin the range of from 50 to 1000 m²/g, preferably from 100 to 950m²/g. Sols of silica-based particles these types also encompass modifiedsols like aluminium-containing silica-based sols and boron-containingsilica-based sols. Preferably, the silica-based particles are present ina sol having an S-value in the range of from 8 to 45%, preferably from10 to 30%, containing silica-based particles with a specific surfacearea in the range of from 300 to 1000 m²/g, suitably from 500 to 950m²/g, and preferably from 750 to 950 m²/g, which sols can be modifiedwith aluminium and/or boron as mentioned above. For example, theparticles can be surface-modified with aluminium to a degree of from 2to 25% substitution of silicon atoms. The S-value can be measured andcalculated as described by Iter & Dalton in J. Phys. Chem. 60(1956),955-957. The S-value indicates the degree of aggregate or microgelformation and a lower S-value is indicative of a higher degree ofaggregation.

[0025] In yet another preferred embodiment of the invention, thesilica-based particles are selected from polysilicic acid and modifiedpolysilicic acid having a high specific surface area, suitably aboveabout 1000 m²lg. The specific surface area can be within the range offrom 1000 to 1700 m²/g and preferably from 1050 to 1600 m²/g. The solsof modified polysilicic acid can contain other elements, e.g. aluminiumand/or boron, which can be present in the aqueous phase and/or in thesilica-based particles. In the art, polysilicic acid is also referred toas polymeric silicic acid, polysilicic acid microgel, polysilicate andpolysilicate microgel, which are all encompassed by the term polysilicicacid used herein. Aluminium-containing compounds of this type arecommonly also referred to as poly-aluminosilicate andpolyaluminosilicate microgel, which are both encompassed by the termscolloidal aluminium-modified silica and aluminium silicate used herein.

[0026] Clays of the smectite type that can be used in the process of theinvention are known in the art and include naturally occurring,synthetic and chemically treated materials. Examples of suitablesmectite clays include montmorillonite/bentonite, hectorite, beidelite.nontronite and saponite, preferably bentonite and especially suchbentonite which after swelling preferably has a surface area of from 400to 800 m²/g. Suitable clays are disclosed in U.S. Pat. Nos. 4,753,710;5,071,512; and 5,607,552, which are hereby incorporated herein byreference.

[0027] Anionic organic particles that can be used according to theinvention include highly cross-linked anionic vinyl addition polymers,suitably copolymers comprising an anionic monomer like acrylic acid,methacrylic acid and sulfonated or phosphonated vinyl addition monomers,usually copolymerized with nonionic monomers like (meth)acrylamide,alkyl (meth)acrylates, etc. Useful anionic organic particles alsoinclude anionic condensation polymers, e.g. melamine-sulfonic acid sols.

[0028] In addition to the cationic organic polymer having a hydrophobicgroup and the anionic microparticulate material, the drainage andretention aids (agents) according to the present invention may alsocomprise further components such as, for example, low molecular weightcationic organic polymers and/or aluminium compounds. The term “drainageand retention aids”, as used herein, refers to two or more components(aids, agents or additives) which, when being added to a stock, givebetter drainage and/or retention than is obtained when not adding thecomponents.

[0029] Low molecular weight (hereinafter LMW) cationic organic polymersthat can be used include those commonly referred to and used as anionictrash catchers (ATC). ATC's are known in the art as neutralizing and/orfixing agents for detrimental anionic substances present in the stockand the use thereof in combination with drainage and retention aidsoften provide further improved drainage and/or retention. The LMWcationic organic polymer can be derived from natural or syntheticsources, and preferably it is an LMW synthetic polymer. Suitable organicpolymers of this type include LMW highly charged cationic organicpolymers such as polyamines, polyamidoamines, polyethyleneimines, homo-and copolymers based on diallyidimethyl ammonium chloride,(meth)acrylamides and (meth)acrylates. In relation to the molecularweight of the main polymer, the molecular weight of the LMW cationicorganic polymer is usually lower, it is suitably at least 2,000 andpreferably at least 10,000. The upper limit of the molecular weight isusually about 700,000, suitably about 500,000 and preferably about200,000.

[0030] Aluminium compounds that can be used according to this inventioninclude alum, aluminates, aluminium chloride, aluminium nitrate andpolyaluminium compounds, such as polyaluminium chlorides, polyaluminiumsulphates, polyaluminium compounds containing both chloride and sulphateions, polyaluminium silicate-sulphates, and mixtures thereof. Thepolyaluminium compounds may also contain other anions than chlorideions, for example anions from sulfuric acid, phosphoric acid, organicacids such as citric acid and oxalic acid.

[0031] The components of drainage and retention aids according to theinvention can be added to the stock in conventional manner and in anyorder. It is preferred to add the main polymer to the stock beforeadding the anionic microparticulate material, even if the opposite orderof addition may be used. It is further preferred to add the main polymerbefore a shear stage, which can be selected from pumping, mixing,cleaning, etc., and to add the anionic particles after that shear stage.When using an LMW cationic organic polymer and/or an aluminium compound,such components are preferably introduced into the stock prior tointroducing the main polymer and anionic microparticulate material.Alternatively, the LMW cationic organic polymer and the main polymer canbe introduced into the stock essentially simultaneously, eitherseparately or in admixture, e.g. as disclosed in U.S. Pat. No.5,858,174, which is hereby incorporated herein by reference.

[0032] The components of the present drainage and retention aids areadded into the stock to be dewatered in amounts which can vary withinwide limits depending on, inter alia, type and number of components,type of furnish, filler content, type of filler, point of addition, saltcontent, etc. Generally the components are added in an amount that givebetter drainage and/or retention than is obtained when not adding thecomponents. The main polymer is usually added in an amount of at least0.001%, often at least 0.005% by weight, based on dry stock substance,and the upper limit is usually 3% and suitably 1.5% by weight. Theanionic microparticulate material is usually added in an amount of atleast 0.001% by weight, often at least 0.005% by weight, based on drysubstance of the stock, and the upper limit is usually 1.0% and suitably0.6% by weight. When using anionic silica-based particles, the totalamount added is suitably within the range of from 0.005 to 0.5% byweight, calculated as SiO₂ and based on dry stock substance, preferablywithin the range of from 0.01 to 0.2% by weight. When using an LMWcationic organic polymer in the process, it can be added in an amount ofat least 0.05%, based on dry substance of the stock to be dewatered.Suitably, the amount is in the range of from 0.07 to 0.5%, preferably inthe range from 0.1 to 0.35%. When using an aluminium compound in theprocess, the total amount introduced into the stock to be dewatered isdependent on the type of aluminium compound used and on other effectsdesired from it. It is for instance well known in the art to utilisealuminium compounds as precipitants for rosin-based sizing agents. Thetotal amount added is usually at least 0.05%, calculated as Al₂O₃ andbased on dry stock substance. Suitably the amount is in the range offrom 0.5 to 3.0%, preferably in the range from 0.1 to 2.0%.

[0033] The process of the invention is preferably used in themanufacture of paper from a suspension containing cellulosic fibres, andoptional fillers, having a high conductivity Usually, the conductivityof the stock that is dewatered on the wire is at least 0.75 mS/cm,suitably at least 2.0 mS/cm, preferably at least 3.5 mS/cm. Very goodresults have been observed at conductivity levels above 5.0 mS/cm andeven above 7.5 mS/cm. Conductivity can be measured by standard equipmentsuch as, for example a WTW LF 539 instrument supplied by ChristianBerner. The values referred to above are suitably determined bymeasuring the conductivity of the cellulosic suspension that is fed intoor present in the headbox of the paper machine or, alternatively, bymeasuring the conductivity of white water obtained by dewatering thesuspension. High conductivity levels mean high contents of salts(electrolytes), where the various salts can be based on mono-, di- andmultivalent cations like alkali metals, e.g. Na⁺ and K⁺, alkalineearths, e.g. Ca²⁺ and Mg²⁺, aluminium ions, e.g. Al³⁺, Al(OH)²⁺ andpolyaluminium ions, and mono-, di- and multivalent anions like halides,e.g., Cl⁻ sulfates, e.g. SO₄ ²⁻ and HSO₄ ⁻, carbonates, e.g. CO₃ ²⁻ andHCO₃ ⁻, silicates and lower organic acids. The invention is particularlyuseful in the manufacture of paper from stocks having high contents ofsalts of di- and multivalent cations, and usually this content is atleast 200 ppm, suitably at least 300 ppm and preferably at least 400ppm. The salts can be derived from the cellulosic fibres and fillersused to form the stock, in particular in integrated mills where aconcentrated aqueous fibre suspension from the pulp mill normally ismixed with water to form a dilute suspension suitable for papermanufacture in the paper mill. The salt may also be derived from variousadditives introduced into the stock, from the fresh water supplied tothe process, or be added deliberately, etc. Further, the content ofsalts is usually higher in processes where white water is extensivelyrecirculated, which may lead to considerable accumulation of salts inthe water circulating in the process.

[0034] Accordingly, the invention is further suitably used inpapermaking processes where white water is extensively recirculated(recycled), i.e. with a high degree of white water closure, for examplewhere from 0 to 30 tons of fresh water are used per ton of dry paperproduced, usually less than 20, suitably less than 15, preferably lessthan 10 and notably less than 5 tons of fresh water per ton of paper.Recirculation of white water obtained in the process suitably comprisesmixing the white water with cellulosic fibres and/or optional fillers toform a suspension to be dewatered; preferably it comprises mixing thewhite water with a suspension containing cellulosic fibres, and optionalfillers, before the suspension enters the forming wire for dewatering.The white water can be mixed with the suspension before, between orafter introducing the drainage and retention aids. Fresh water can beintroduced in the process at any stage; for example, it can be mixedwith cellulosic fibres in order to form a suspension, and it can bemixed with a suspension containing cellulosic fibres to dilute it so asto form the suspension to be dewatered, before or after mixing the stockwith white water and before, between or after introducing the drainageand retention aids.

[0035] Further additives which are conventional in papermaking can ofcourse be used in combination with the additives according to theinvention, such as, for example, dry strength agents, wet strengthagents, sizing agents, e.g. those based on rosin, ketene dimers and acidanhydrides, optical brightening agents, dyes, etc. The cellulosicsuspension, or stock, can also contain mineral fillers of conventionaltypes such as, for example, kaolin, china clay, titanium dioxide,gypsum, talc and natural and synthetic calcium carbonates such as chalk,ground marble and precipitated calcium carbonate.

[0036] The process of this invention is used for the production ofpaper. The term “paper”, as used herein, of course include not onlypaper and the production thereof, but also other sheet or web-likeproducts, such as for example board and paperboard, and the productionthereof. The process can be used in the production of paper fromdifferent types of suspensions of cellulose-containing fibres and thesuspensions should suitably contain at least 25% by weight andpreferably at least 50% by weight of such fibres, based on drysubstance. The suspensions can be based on fibres from chemical pulpsuch as sulphate, sulphite and organosolv pulps, mechanical pulp such asthermomechanical pulp, chemo-thermomechanical pulp, refiner pulp andgroundwood pulp, from both hardwood and soft-wood, and can also be basedon recycled fibres, optionally from de-inked pulps, and mixturesthereof.

[0037] The invention is further illustrated in the following Exampleswhich, however, are not intended to limit the same. Parts and % relateto parts by weight and % by weight, respectively, unless otherwisestated.

EXAMPLE 1

[0038] Cationic polymers were prepared by polymerizing a monomer mixtureaccording to the following general procedure:

[0039] Monomers and an initiator, 2,2′-azobis(2-amidinopropane)dihydrochloride (Wako V-50) were added to an aqueous phase andpolymerization was carried out for about 24 hours at 45° C. withstirring under a nitrogen atmosphere. The cationic polymer, which wasobtained as a clear gel, was dissolved in water and used as an 0.1%aqueous solution.

[0040] Polymers according to the invention, P1 to P5, and polymersintended for comparison purposes, Ref. 1 and Ref. 2, were prepared fromthe indicated monomers in the indicated amounts:

[0041] P1: acrylamide (90 mole %), and

[0042] acryloxyethyl dimethyl n-butylammonium chloride (10 mole %);

[0043] P2: acrylamide (90 mole %) and

[0044] acryloxyethyl dimethyl methylcyclohexylammonium chloride (10 mole%);

[0045] P3: acrylamide (90 mole %),

[0046] methacryloxyaminopropyl trimethylammonium chloride (5 mole %),and

[0047] methacryloxyethyl t-butylamine (5 mole %);

[0048] P4: acrylamide (90 mole %),

[0049] methacryloxyaminopropyltrimethylammonium chloride (5 mole %), and

[0050] N-isopropylacrylamide (5 mole %);

[0051] P5: acrylamide (90 mole %),

[0052] methacryloxyaminopropyltrimethylammonium chloride (5 mole %), and

[0053] N-t-butylacrylamide (5 mole %);

[0054] Ref. 1: acrylamide (90 mole %), and

[0055] acryloxyethyl trimethylammonium chloride (10 mole %).

[0056] Ref. 2: acrylamide (95 mole %), and

[0057] acryloxyethyl trimethylammonium chloride (5 mole %).

EXAMPLE 2

[0058] Drainage and retention performance was evaluated by means of aDynamic Drainage Analyser (DDA), available from Akribi, Sweden, whichmeasures the time for draining a set volume of stock through a wire whenremoving a plug and applying vacuum to that side of the wire opposite tothe side on which the stock is present. First pass retention wasevaluated by measuring, with a nephelometer, the turbidity of thefiltrate, the white water, obtained by draining the stock.

[0059] The furnish used was based on 56% by weight of peroxide bleachedTMP/SGW pulp (80/20), 14% by weight of bleached birch/pine sulphate pulp(60/40) refined to 200° CSF and 30% by weight of china clay. To thestock was added 40 g/l of a colloidal fraction, bleach water from an SCmill, filtrated through a 5 μm screen and concentrated with an UFfilter, cut off 200,000. Stock volume was 800 ml, consistency 0.14% andpH 7.0. Conductivity was adjusted to about 2.5 mS/cm by addition ofcalcium chloride (400 ppm Ca).

[0060] The stock was stirred in a baffled jar at a speed of 1500 rpmthroughout the test and additions were conducted as follows: i) addingcationic polymer to the stock following by stirring for 30 seconds, ii)adding anionic microparticulate material to the stock followed bystirring for 15 seconds, iii) draining the stock while automaticallyrecording the drainage time.

[0061] The cationic polymers tested in this Example were P1 and Ref. 1according to in Example 1. The anionic microparticulate material used inthis Example was a sol of silica-based particles of the type disclosedin U.S. Pat. No. 5,368,833. The sol had an S-value of about 25% andcontained silica particles with a specific surface area of about 900m²/g which were surface-modified with aluminium to a degree of 5%. Thesilica-based sol was added to the stock in an amount of 1.5 kg/ton,calculated as SiO₂ and based on dry stock system.

[0062] Table 1 shows the drainage time and retention values at variousdosages of P1 and Ref. 1, calculated as dry polymer on dry stock system(kg/ton). TABLE 1 Dewatering time (sec)/ Cationic Turbidity (NTU) atindicated Polymer dosage Polymer 0.5 kg/t 1.0 kg/t 1.5 kg/t 2.0 kg/t P111.6/48 8.9/34 5.8/32 4.7/14 Ref. 1 12.0/57 9.0/49 6.5/36 5.1/28

EXAMPLE 3

[0063] In this test series, dewatering and retention performance wasevaluated according to the procedure described in Example 2.

[0064] The furnish was the same as used in Example 2. Stock volume was800 ml, pH about 7 and conductivity was adjusted to 7.0 mS/cm byaddition of calcium chloride (1300 ppm Ca), thus simulating a highelectrolyte content and a high degree of white water closure.

[0065] The anionic inorganic material according to Example 2 weresimilarly used in this Example and was added in an amount of 1.5 kg/ton,calculated as SiO₂ and based on dry stock system.

[0066] The polymers used in this Example were P1, P2 and Ref. 1according to Example 1. Table 2 shows the dewatering and retentioneffect at various dosages of P1, P2 and Ref. 1, calculated as drypolymer on dry stock system. TABLE 2 Dewatering time (sec)/ CationicTurbidity (NTU) at indicated Polymer dosage of Polymer 0.5 kg/t 1.0 kg/t1.5 kg/t 2.0 kg/t P1 11.0/— 8.7/49 6.3/40 6.0/38 P2 10.7/— 7.9/50 6.1/435.5/32 Ref. 1 12.1/— 9.5/57 8.8/47 7.8/43

EXAMPLE 6

[0067] In this test series, dewatering and retention performance wasevaluated according to the procedure described in Example 2.

[0068] The furnish was the same as used in Example 2. Stock volume was800 ml and pH about 7. Sodium chloride (550 ppm Na) and calcium chloridewere added to the stock to adjusted the conductivity to 5.0 mS/cm (400ppm Ca) and 7.0 mS/cm (1300 ppm Ca).

[0069] The polymers P2, P3, Ref. 1 and anionic microparticles accordingto Example 1 were similarly used in this test series in conjunction witha low molecular weight cationic polyamine. The polyamine was added tothe stock followed by stirring for 30 seconds before addition of thecationic acrylamide-based polymer. The polyamine was added in an amountof 3 kg/ton, calculated as dry polymer on dry stock system. The mainpolymers P2, P3 and Ref. 1 were added in an amount of 1.5 kg/ton,calculated as dry polymer on dry stock system.

[0070] Table 5 shows the dewatering and retention effect at variousconductivities and dosages of silica-based particles, calculated as SiO₂and based on dry stock system. TABLE 5 Test SiO₂ Dewatering time(sec)/Turbidity (NTU) Series Dosage Conductivity by using the indicatedCationic Polymer No. (kg/t) (mS/cm) P2 P3 Ref. 1 1 1.5 5.0 6.9/— —/39 7.2/51 2 1.5 7.0 16.2/— —/56 24.7/60 3 1.0 7.0 7.8/— —/50 13.3/55

EXAMPLE 7

[0071] In this test series, dewatering and retention performance wasevaluated according to the procedure described in Example 2.

[0072] The furnish was the same as used in Example 2. Stock volume was800 ml and pH about 7. Varying amounts of sodium chloride was added tothe stock to adjust the conductivity to 2.5 mS/cm (550 ppm Na) (TestSeries Nos. 1-3), 5.0 mS/cm (1470 ppm Na) (Test Series Nos. 4-6) and10.0 mS/cm (3320 ppm Na) (Test Series Nos. 7-9).

[0073] The cationic polymers used were P1 to P3 and Ref. 1 according toExample. 1. The anionic microparticulate material used was hydratedsuspension of powdered Na-bentonite in water.

[0074] Table 6 shows the dewatering and retention effect at variousdosages of cationic polymer, calculated as dry polymer on dry stocksystem, and bentonite, calculated as dry on dry stock system.

EXAMPLE 4

[0075] In this test series, dewatering and retention performance wasevaluated according to the procedure described in Example 2.

[0076] The stock used in this Example was similar to the stock usedaccording to Example 3 and had a conductivity of about 7.0 mS/cm (1300ppm Ca). The anionic inorganic material according to Example 2 was addedin an amount of 1.5 kg/ton, calculated as SiO₂ and based on dry stocksystem. The polymers used were P3 and Ref. 1 according to Example 1.

[0077] Table 3 shows the results of the dewatering tests at variousdosages of P3 and Ref. 1, calculated as dry polymer on dry stock system.TABLE 3 Cationic Dewatering time (sec) at Polymer dosage of Polymer 0.5kg/t 1.0 kg/t 1.5 kg/t 2.0 kg/t P3 13.2 10.0 7.4 5.6 Ref. 1 15.5 12.110.6 10.2

EXAMPLE 5

[0078] In this test series, the dewatering performance was evaluatedaccording to the procedure described in Example 2.

[0079] The stock used in this test series was similar to the oneaccording to Example 2 and had a conductivity of about 2.5 mS/cm. Thepolymers used were P4, P5 and Ref. 2 according to Example 1 which wereadded in an amount of 2 kg/ton, calculated as dry polymer on dry stocksystem. The anionic inorganic material according to Example 2 wassimilarly used in this test series.

[0080] Table 4 shows the results of the dewatering tests at variousdosages of anionic inorganic material, calculated as SiO₂ and based ondry stock system. TABLE 4 Cationic Dewatering time (sec) at SiO₂ dosageof Polymer 0.5 kg/t 1.0 kg/t 1.5 kg/t 2.0 kg/t P4 11.3 10.1 9.8 9.1 P511.8 9.5 8.8 8.5 Ref. 2 11.9 10.7 10.3 9.9

[0081] TABLE 6 Test Polymer Bentonite Dewatering time (sec)/Turbidity(NTU) Series Dosage Dosage by using the indicated Cationic Polymer No.(kg/t) (kg/t) P1 P2 P3 Ref. 1 1 2 4 6.6/25 8.5/— 7.5/— 8.9/39 2 2 86.3/29 7.9/— 7.2/— 8.3/37 3 4 8 4.2/10 4.6/— 4.9/— 8.4/15 4 2 4 7.0/308.4/— 8.9/— 8.8/42 5 2 8 6.6/28 8.0/— 8.4/— 8.6/40 6 4 8 4.8/10 5.0/—4.8/— 6.6/28 7 2 4 7.9/22 8.0/— 8.2/— 9.1/45 8 2 8 7.4/30 7.2/— 7.1/—8.2/48 9 2 8 5.2/11 4.8/— 5.2/— 7.5/28

1. A process for the production of paper from a suspension containingcellulosic fibres, and optional fillers, comprising adding to thesuspension drainage and retention aids comprising a cationic organicpolymer and anionic microparticulate material, forming and dewateringthe suspension on a wire, characterised in that the cationic organicpolymer has a non-aromatic hydrophobic group.
 2. A process according toclaim 1, characterised in that the cationic organic polymer is a vinyladdition polymer comprising in polymerized form one or more monomerscomprising at least one cationic monomer having a non-aromatichydrophobic group.
 3. A process according to claim 1 or 2, characterisedin that the cationic organic polymer is a vinyl addition polymercomprising in polymerized form at least one non-cationic monomer havinga non-aromatic hydrophobic group and at least one cationic monomer.
 4. Aprocess according to claim 1, 2 or 3, characterised in that thehydrophobic group is attached to a nitrogen or oxygen which, in turn, isattached to the polymer backbone via a chain of atoms.
 5. A processaccording to claim 1, 2, 3 or 4, characterised in that the hydrophobicgroup is an alkyl group containing from 3 to 12 carbon atoms.
 6. Aprocess according to any of the preceding claims, characterised in thatthe cationic organic polymer is an acrylamide-based polymer.
 7. Aprocess according to any of the preceding claims, characterised in thatthe cationic organic polymer comprises in polymerized form a cationicmonomer having a non-aromatic hydrophobic group represented by thegeneral formula (I):

wherein R₁ is H or CH₃; R₂ and R₃ are each an alkyl group having from 1to 2 carbon atoms; A is O or NH; B is an alkylene group of from 2 to 8carbon atoms or a hydroxy propylene group; R₄ is a substituentcontaining an alkyl group containing from 4 to 8 carbon atoms; and X⁻ isan anionic counterion.
 8. A process according to any of the precedingclaims, characterised in that the cationic organic polymer comprises inpolymerized form a non-ionic monomer having a non-aromatic hydrophobicgroup represented by the general formula (IV):

wherein R₁ is H or CH₃; A is O or NH; B is an alkylene group of from 2to 8 carbon atoms or a hydroxy propylene group or, alternatively, A andB are both nothing whereby there is a single bond between C and N(O═C—NR₈R₉); R₈ and R₉ are each H or a substituent containing an alkylgroup having from 1 to 6 carbon atoms, at least one of R₈ and R₉ being asubstituent containing an alkyl group having from 2 to 6 carbon atoms.9. A process according to any of the preceding claims, characterised inthat the cationic organic polymer comprises in polymerized form anon-ionic monomer having a non-aromatic hydrophobic group represented bythe general formula (V):

wherein R₁ is H or CH₃; A is O; B is an alkylene group of from 2 to 4carbon atoms; n is an integer of at least 1; R₁₀ is alkyl having atleast 2 carbon atoms.
 10. A process according to any of the precedingclaims, characterised in that the cationic organic polymer is a vinyladdition polymer prepared from a monomer mixture comprising from 5 to 25mole % of monomer having a non-aromatic hydrophobic group, and from 95to 75 mole % of other copolymerizable monomers.
 11. A process accordingto any of the preceding claims, characterised in that the anionicmicroparticulate material is selected from silica-based particles andbentonite.
 12. A process according to any of the preceding claims,characterised in that the drainage and retention aids further comprisesa low molecular weight cationic organic polymer.
 13. A process accordingto any of the preceding claims, characterised in that the suspensionthat is dewatered on the wire has a conductivity of at least 2.0 mS/cm.14. A process according to any of the preceding claims, characterised inthat the process further comprises dewatering the suspension on a wireto obtain a wet web of paper and white water, recirculating the whitewater and optionally introducing fresh water to form a suspensioncontaining cellulosic fibres, and optional fillers, to be dewatered,wherein the amount of fresh water introduced is less than 30 tons perton of dry paper produced.
 15. A process according to any of thepreceding claims, characterised in that less than 10 tons of fresh wateris introduced into the process per ton of dry paper produced.
 16. Acationic vinyl addition polymer comprising in polymerized form at leastone non-cationic monomer having a non-aromatic hydrophobic group and atleast one cationic monomer.
 17. A cationic vinyl addition polymeraccording to claim 16, characterised in that the hydrophobic group isattached to a nitrogen or oxygen which, in turn, is attached to thepolymer backbone via a chain of atoms.
 18. A cationic vinyl additionpolymer according to claim 16 or 17, characterised in that thehydrophobic group is an alkyl group containing from 3 to 12 carbonatoms.
 19. A cationic vinyl addition polymer according to claim 16, 17or 18, characterised in that the cationic vinyl addition polymer is anacrylamide-based polymer.
 20. A cationic vinyl addition polymeraccording to claim 16, 17, 18 or 19, characterised in that the cationicvinyl addition polymer comprises in polymerized form a non-ionic monomerhaving a non-aromatic hydrophobic group represented by the generalformula (IV):

wherein R₁ is H or CH₃; A is O or NH; B is an alkylene group of from 2to 8 carbon atoms or a hydroxy propylene group or, alternatively, A andB are both nothing whereby there is a single bond between C and N(O═C—NR₈R₉); R₈ and R₉ are each H or a substituent containing an alkylgroup having from 1 to 6 carbon atoms, at least one of R₈ and R₉ being asubstituent containing an alkyl group having from 2 to 6 carbon atoms.21. A cationic vinyl addition polymer according to any of claims 16 to20, characterised in that the cationic vinyl addition polymer comprisesin polymerized form a non-ionic monomer having a non-aromatichydrophobic group represented by the general formula (V):

wherein R₁ is H or CH₃; A is O or NH; B is an alkylene group of from 2to 4 carbon atoms; n is an integer of at least 1; R₁₀ is alkyl having atleast 2 carbon atoms.
 22. A cationic vinyl addition polymer according toany of claims 16 to 21, characterised in that the cationic vinyladdition polymer comprises in polymerized form a cationic monomerrepresented by the general formula (I):

wherein R₁ is H or CH₃; R₂ and R₃ are each H or an alkyl group havingfrom 1 to 3 carbon atoms; A is O or NH; B is an alkylene group of from 2to 4 carbon atoms or a hydroxy propylene group; R₄ is a non-aromatichydrocarbon group containing from 4 to 8 carbon atoms; and X⁻ is ananionic counterion.
 23. A cationic vinyl addition polymer according toany of claims 16 to 22, characterised in that the cationic vinyladdition polymer comprises in polymerized form a cationic monomerrepresented by the general formula (III):

wherein R₁ is H or CH₃; R₂ and R₃ are each H or an alkyl group havingfrom 1 to 3 carbon atoms, suitably 1 to 2 carbon atoms; A is O or NH; Bis an alkylene group of from 2 to 8 carbon atoms, suitably 2 to 4 carbonatoms, or a hydroxy propylene group; R₇ is H, an alkyl group having from1 to 3 carbon atoms, a benzyl group or a phenylethyl group; and X⁻ is ananionic counterion.
 24. A cationic vinyl addition polymer according toany of claims 16 to 23, characterised in that the cationic vinyladdition polymer is prepared from a monomer mixture comprising from 5 to25 mole % of non-ionic monomer having a non-aromatic hydrophobic group,and from 95 to 75 mole % of other copolymerizable monomers.